The purpose of this work is to examine the biological and immunological properties of histocompatibility antigens (H-2) and tumor specific transplantation antigens (TSTA) and, ultimately, to purify the molecules expressing these antigens. The approach is to purify both antigens from a single cell source (RBL-5) and determine their antigenic properties at each stage of purification. The antigenic properties monitored include: 1) ability to induce transplantation rejection, 2) ability to evoke a humoral response, 3) ability to interact with syngeneic or xenogeneic antisera. At the same time H-2 and TSTA with different biological properties from other sources are purified and compared with the antigens from RBL-5. The rationale for this approach is that through purification of the antigens from a single source one can learn the relationship, if any, of TSTA to H-2 and to what extent the properties of these antigens depend on the structure of the intact cell membrane. Furthermore, any unusual structural properties of H-2 and TSTA from other sources, when compared with the structure of their counterparts from RBL-5, may shed light on the molecular basis for the biological activity of these antigens.